Compressed Air Energy Storage (CAES): Part 2

If such reserviors exist for energy storage using cpressed gas why not use them for CO2 sequestration?

CES = Hey Cheech—here’s an idea:  Lets drill a hole and blow some hi pressure air into it.  The fact we know nothing about where this pressure will ultimately go, or how it might affect existing underground structures makes no difference.  The fact we don’t know what the “reservoir” its going into looks like or how its shaped is irrelevant.  If it mixes with some underground gas or water, or fractures a formation that blows out of the ground somewhere else is of no concern (unless it happens to blow our house off the ground) .  Out of sight, out of mind.

I love this idea.  and don’t forget—Puff puff pass….

We have some engineering-based analysis of CAES here:
http://dotyenergy.com/Markets/CAES.htm
There are plenty of good reasons why there have been only two demonstrations of CAES on this planet in the past three decades, and won’t be more than a few more in the next three decades.
We’ll be presenting a paper at the ASME ES2010 conference in May that takes a more careful look at energy storage options than we’ve seen in other articles thus far.

The abstract follows:
There is the general perception that increased grid-scale energy storage will facilitate expansion of renewables.  Most discussions of costs and competitiveness of storage options have addressed cycle efficiency and capital costs of energy storage in terms of both $/kW and $/kWhr.  However, likely number of cycles per year, marginal value of delivered energy, impact on GHG emissions, application-specific expected lifetime, discount rate, likely trends in the markets, and other factors have seldom been addressed, at least for grid-scale applications. 

The levelized costs of delivered energy from the leading technologies for grid-scale energy storage are calculated using a model that considers likely number of cycles per year, application-specific expected lifetime, discount rate, duty cycle, and likely trends in the markets.  The expected capital costs of the various options evaluated – pumped hydrostorage, underground pumped hydrostorage (UPHS), advanced adiabatic compressed air energy storage (AA-CAES), carbon-lead-acid batteries, hydrogen fuel cells, lead-acid batteries, lithium-ion batteries, flywheels, sodium sulfur batteries, ultra capacitors, and superconducting magnetic energy storage (SMES) – are based on recent installation cost data to the extent possible.  The marginal value of the delivered stored energy is analyzed using recent grid energy prices from regions of high wind-energy penetration. 

Grid-scale energy storage is expected to lead to significant reductions in GHG emissions only in regions where the off-peak energy is very clean.  These areas will be characterized by a high level of wind energy with cheap off-peak and peak prices.  At the expected daily price differentials, the only conventional options expected to be commercially viable are hydro storage and UPHS.  The market value of energy storage for short periods of time (under a few hours) is expected to be minimal for grid-scale purposes.  Only low-cost daily storage is easily justified both from an economic and environmental perspective.

A lesser-known energy storage option, Windfuels, is also briefly reviewed.  Here, excess off-peak electrical energy is used to synthesize standard liquid fuels, such as gasoline and jet fuel, from CO2 and H2O.  Simulations have shown that innovations should make it practical to reduce CO2 to CO at 90% of theoretical efficiency limits.  When combined with other process advances, it should then be possible to synthesize hydrocarbons and alcohols from point-source CO2 and off-peak clean grid energy (wind or nuclear) at system efficiencies in the range of 51-59%. The cost of the tanks for storing energy in jet fuel, ethanol, and diesel is only $0.02/kWhr.  The cost of storing vast amounts of energy in batteries, compressed air, or flywheels would be several thousand times greater.

David Doty